Twitter COO Dick Costolo has been given the reigns of the company, taking over the position of CEO from site co-founder Evan Williams.

Williams writes of the decision:

The challenges of growing an organization so quickly are numerous. Growing big is not success, in itself. Success to us means meeting our potential as a profitable company that can retain its culture and user focus while having a positive impact on the world. This is no small task. I frequently reflect on the type of focus that is required from everyone at Twitter to get us there.

This led to a realization as we launched the new Twitter. I am most satisfied while pushing product direction. Building things is my passion, and I’ve never been more excited or optimistic about what we have to build.

This is why I have decided to ask our COO, Dick Costolo, to become Twitter’s CEO. Starting today, I’ll be completely focused on product strategy.

@ev announced today on the Twitter blog that the microblogging company works at implementing an Phase 1 of the official Retweet project. Although details haven’t been finalized yet, Evan Williams showed a sketch of the possible future integration, all while admitting that the users and the Twitter community basically decide what Twitter becomes.

Retweeting is a great example of Twitter teaching us what it wants to be. The open exchange of information can have a positive global impact and the more efficient dissemination of information across the entire Twitter ecosystem is something we very much want to support. That’s why we’re planning to formalize retweeting by officially adding it to our platform and Twitter.com. read more

The UK is second only to the US in Twitter usage, with London topping the chart, according to Evan Williams, interviewed for BBC2’s Newsnight program.

Although official statistics aren’t available, the BBC’s research suggests that an estimated three million Brits joined Twitter in the past year, with as many signing up to follow friends as to keep tabs on their favorite celebrities.

Williams played down the accusation that Twitter could lead to the breakdown of community, saying that anyone who believed that obviously hadn’t used the service. read more